1. Field of the Invention
The present invention relates generally to techniques for forming electrical connections and, more particularly, to a method and apparatus for attaching electrical accessories to electrical cords at very high speeds.
2. Description of the Prior Art
Various techniques have been proposed for connecting an electrical accessory to an electrical conductor included as part of an electrical cord. A common attachment technique is to strip the insulation from a portion of the conductor and secure the exposed conductor to an electrically conductive portion of the accessory. For convenience, electrically conductive portions of accessories hereafter will be referred to as electrical leads. In the case of an accessory such as a miniature lamp used in decorative string sets, these leads typically take the form of thin, to elongated, easily bent wire.
The connection between the conductors and the leads commonly is made by crimping the leads and the conductors together, by soldering, or by clamping through the use of various fasteners. These conventional techniques have certain drawbacks. A certain amount of effort is required to strip the insulative material from the conductor. Thereafter, the conductors and the leads must be aligned and a suitable fastening process carried out. Because the leads often are easily bent, they must be handled with care during the connection process. Moreover, if the conductor is made of multiple strands, the conductor also must be handled carefully to avoid damage to the individual strands. With respect to decorative string sets, it is not unusual for as many as eight separate steps to be required to properly and reliably connect a miniature lamp to an electrical cord.
In order to overcome the time-consuming steps associated with assembly of such string sets, specially configured sockets and plug-in lamp bases have been designed. An effective design of this type is shown in the String Set Patent. Even in the String Set Patent, however, a certain amount of assembly time is required to strip the conductors and assemble them into a specially configured socket. In short, although proposals such as the String Set Patent permit relatively easy connection of the conductors and the leads, the basic problem of numerous assembly steps still exists.
A different approach has been suggested in the Electrical Connection Patent. There, an electrical conductor was carried on the surface of an insulative member such as a circuit board. Because the conductor was carried on the surface of the circuit board, the conductor was exposed. Accordingly, no insulative material needed to be stripped from the conductor in order to have access to the conductor. In one embodiment, an electrical lead was placed on the opposite side of the circuit board from the conductor and the electrical lead was driven and bent sideways into and through the circuit board to cause the lead to engage and make electrical contact with the underside of the conductor. In another embodiment, the lead was placed on the same side of the circuit board as the conductor and spaced portions of the lead were driven into the circuit board such that an intermediate portion of the lead came into contact with the conductor. These results were brought about by employing a heated or ultrasonically vibrated tool member which not only engaged the lead, but also displaced portions of the circuit board in the region of the tool member. After electrical contact between the lead and the conductor was established, the tool member was withdrawn and portions of the lead remained embedded in the insulative member.
Although the foregoing technique as described in the Electrical Connection Patent has been highly successful, it still has not addressed certain problems. For example, the patent does not describe how the technique could be used to attach an accessory to an electrical cord. Although the patent at column 7, lines 55-59 states that the invention "is useful for attaching a variety of types of wires, strips, and the like to a conductor carried by a deformable insulative member such as being carried on its surface or embedded within it," the invention clearly is directed to a circuit board-type construction where the conductor is on the surface of the circuit board. There is no suggestion or teaching that the technique could be applied to connect leads to electrical cords per se.